Convective Drying of Rapeseed Hybrids’

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Agriculturae Conspectus Scientifcus | Vol. 74 (2009) No. 3 (191-196)

ORIGINAL SCIENTIFIC PAPER

Summary

Te aim o this study was to investigate the water release rom seeds o threerape hybrids, (Artus, Baldur and itan), during the convection drying o theseeds at three diferent drying temperature (40, 60 and 80 C). Te drying wasconducted in laboratory scale drier which can simulate the conditions o largedrier. Te air velocity in the drier was maintained at 1.0 m/s. Activation energyneeded or starting the process o water release during the convective drying ooil seed rape seeds was also studied.

According to the obtained values, the mathematical models (equations andcurves)o kinematicdrying were determined. By comparing the exponentialequations and the constants o water release rom seeds it was observed thatdrying o hybrid Artus was the slowest and the one o hybrid itan the astest.Results showed that there was a signicant diference between all investigatedhybrids in water release rate and that within the same drying conditions, hybridsshowed diferent behaviour. Moreover, air temperature increase caused signicantincrease in water release rom the seeds. Te highest activation energy neededor starting the process o water release rom the seeds had the hybrid Artus andthe lowest one hybrid itan. Due to this, it can be concluded that the activationenergy was reversely proportional to the water release rate rom the seeds.

Key words

convective drying, oil seed rape, hybrids, activation energy

Convective Drying of Rapeseed HybridsSeeds

eljko JUKI 1( )

ajana KRIKA 2

Milan POSPIIL 1

Neven VOA 2

Nikola BILANDIJA 3

1 University o Zagreb, Faculty o Agriculture, Department o Field Crops, Forage and Grass-land, Svetoimunska 25, 10000 Zagreb, Croatia

e-mail: [email protected] University o Zagreb, Faculty o Agriculture, Department o Agricultura l echnology, Stor-age and ransport, Svetoimunska 25, 10000 Zagreb, Croatia3 University o Zagreb, Faculty o Agriculture, Graduated student, Svetoimunska 25, 10000Zagreb, Croatia

Received: November 17, 2008 | Accepted: April 3, 2009


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Agric. conspec. sci. Vol. 74 (2009) No. 3

192 eljko JUKI, ajana KRIKA, Milan POSPIIL, Neven VOA, Bilandija NIKOLA

Introduction

Te speed and quality o seed drying depend on physi-cal characteristics o the drying environment, physical andchemical characteristics o the material to be dried, and thick-ness o the layer through which the water is difused in thedrying regime. In natural drying process air temperature is

approximately the same as that o the seed and, thus, dryingis slower. With increasing the air temperature, the dryingprocess is accelerated (Krika et al., 2007).

Relevant or drying rate is the rate o water ow throughthe seed towards the surace. Te perormance o the mate-rial during the drying process is essentially inuenced by itscomposition, i.e., by characteristics o diferent parts o theseed. In relation to wheat and corn, rape seed has diferentstructure and shape. Te spherical shape o seed reduces theporosity o the pile to minimum which increases air resist-ance during the drying process.

Exposing wet seeds to higher temperatures or a longer

period o time may lead to a too ast drying and thus to crack-ing, which potentially afects sae storage (Krika et al., 2007).

It is already known that diferent lots o rape seed, withdiferent initial moisture, perorm diferently in the dryingprocess. Aer the drying procedure, the seeds at the dryer's exit have diferent moisture content, which may representa problem during storage. One part o the seed is overdried,which is not rational, either in terms o energy consumptionor in terms o preservation o nutritive substances o theseed (excessive drying o grain or seed increases the proteincontent because o dry matter concentration which reducesdigestibility, i.e., it leads to protein denaturation and lowersolubility), while the seeds parts with moister higher than

needed or sae storage provide the ground or developmento microorganisms (Kati, 1997; BIOEN, 2001).

Te researchers present the mathematical modeling o thedrying process (moisture loss rom seeds) with polynomial,exponential and logarithmic equations.

Tus, Page (1949) proposes exponential equation o thethin layer drying model with characteristic seed constantsand moisture ratios, while Tompson (1967) proposes expo-nential equation with variant valued and dry air tempera-ture. Noomhorm and Vermal (1986) also use second orderexponential equations in studying the thin layer and shap-ing its curve. Tey also compared their own studies with theresults o the Tompson model, aer which they concludedthat the Tompson model gives satisactory results in thinlayer drying. Teory o application o the thin layer dryingprocedure on thick layer was not acceptable until the mid1960-ties, when according to Mujumdar (2000), Hukill in1954 was the rst who started to develop the thick layer simu-lation model on the basis o the results obtained by studyingthe thin layer drying process. Tis development resulted inintroduction o computer-based models or monitoring andsimulation o the process.

However, in order to give ull description o the dryingkinetics it is necessary to know a large number o parameters

(Mujumdar, 2000). Among them are type o dryer, dryers ge-ometry, heating method, but also the properties o the dryingmaterial. It is important to know geometrical particles o thematerial such as size o particles, distribution o particle size,distribution o capillary size and particle shape (Krika et al.,2005). It is particularly important to know transer capaci-

ties o the material. When mass transer is concerned, thesecapacities consist o activation energy or water release romseed and drying constant (Voa et al., 2007). It is necessaryto know the variations o these capacities during the drying.Since all these capacities vary with changing working envi-ronment, it is clear that the modeling o the drying process isa complex task. Especially so, i we keep in mind that duringthe drying process the parallel processes o mass transer andheat transer happen.

Tus, the specic aim o a large number o studies is tond a simple mathematical model that will successully de-scribe the drying kinetics. Tese are mainly exponentialmodels with only ew parameters.

Te main shortcoming o such models is that physical sig-nicance o their parameters has not been determined yet.What is known about these parameters at present is the in-uence o specic conditions and o some properties o thematerial on their values (Sander and Glasnovi, 2004). It wasdetermined that the drying process can be described usingmathematical modeling by exponential, logarithmic or poly-nomial equations, regardless o the variety in question. Tecomparison o the obtained polynomial equations, or inter-relation o incline can be shown by use o derivation dw/d(Martins and Stroshine, 1987; Krika et al., 1999). Te mois-ture content o drying material can be at any moment antic-ipated by use o any o these drying equations, especially i

the drying constant "k" is calculated.Te drying constant is normally in unction o drying air

temperature calculation. Henderson and Pabis (1961) proposedthe equation or calculating the drying constant ollowingthe Arrhenius equation. Tis equation allows to calculate theenergy required or initiating the water release process. TeArrhenius equation puts in relation the drying temperature,water release constant and activation energy or initiating thewater release process. Te activation energy can be determinedby means o drying temperature (), water release constant(k), or, by using the incline ln k and 1/. Consequently, theactivation energy is calculated by multiplying the incline o

the said direction and universal gas constant 8.314 J/mol K.Bala (1997) dened the activation energy or reaction's ac-tivation energy (Ea) o water release rom seed, which must bebrought to the water molecules to stir their inter-reactions. Inorder to incite chemical reaction in the water molecules, theymust collide, but molecules can interact only i their energycharge is above the required activation energy. In chemicalkinetics, activation energy is the level o potential barrierseparating the product rom reactant. Te molecules gainactivation energy by transorming their kinetic energy intopotential energy. Tereore, i water molecules' kinetic energy


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193Convective Drying o Rapeseed Hybrids Seeds

in the seeds is not high enough, it can be ully transormedin to potential energy by their collision, but it will not set onthe activation complex.

Te molecules become distant rom each other as soon aspotential energy decreases. I energy is brought in the seed'smolecule system, e.g., heat energy (by raising temperature),

a larger number o molecules per second will cross the po-tential energy barrier.

In other words, reaction rate in molecule transormationrises with temperature increase. With increasing the poten-tial energy barrier i.e., reaction activation energy, a smallernumber o reacting molecules can cross the peak o energybarriers and the reaction becomes slower (Voa et al., 2007).

Te aim o this study was to investigate the water releaserom seeds o three rape hybrids (Artus, Baldur and itan),during the convection drying o the seeds at three diferentdrying temperatures (40, 60 and 80 C). Since it has been as-sumed that the mentioned hybrids were dried in diferent ways,the diferences in water release rate between the studied rapehybrids were determined, as well as the inuence o dryingtemperature on main parameters o the convection drying.

Materials and methods

Te research was carried out in the laboratory o theDepartment o Agricultural echnology, Storage and ransporto the Faculty o Agriculture o the University o Zagreb onthree "00" rape hybrids: Artus, Baldur and itan, grownin experimental elds in Bjelovar-Bilogorska County during2004, with application o e cient plant growing measures.Since the samples o rapeseeds had diferent initial mois-ture and these values had to be equalized in order to make

the samples comparable or urther studies. For this reason,the samples were rehydrated up to about 18% o moisturecontent. Beore drying, the samples were cleared o impuri-ties and oreign matters. Te rehydration was carried out bydirect action on seed mass with precisely determined quantityo distilled water. Te quantity o water needed or desiredmoisture level (18%) was determined ollowing the expres-sion rom the Measurement Instructions o the State O ceo Metrology (Pliesti and Varga, 1995).

Ten, the samples were stored in glass vessels and put inthe cooling chamber at temperatures rom 3 to 5 C, in du-ration o 72 hours, during which time they were requentlystirred. Aer conditioning, the moisture content in the sam-

ples was determined again, and the rehydrated samples werepositioned as the initial ones and were used in urther work.

Te drying was perormed in the laboratory scale dryero small capacity but with capacity to simulate the condi-tions present in large dryer. Te airow rate in the dryer wasmaintained at 1.0 m/s, and the samples were dried at threediferent temperatures, i.e., 40 C, 60 C and 80 C, that werechosen because o their practical value.

Beore drying the water content in the seed sample wasdetermined. Aer that the seed mass at the end o the dryingprocess was mathematically determined. A digital balance

was placed next to the laboratory scale dryer. Beore eachstart o the drying process, temperature and relative humid-ity were determined by use o a psychrometer placed in thespace o the dryer. Also, beore starting the drying processin the drying space (vessel with perorated bottom) temper-ature o the seeds was determined. Every ve minutes the

vessel was weighted.Te airow rate, or an regulation was also controlledmanually, by use o regulation transormer. Measurement othe preset air temperature was perormed by means o probeP 100 immediately beore the air owed through the sample.Te airow rate aer exiting the sample layer was determinedby means o digital anemometer made by "Edra Five" romUnited Kingdom. Te reading area o the digital anemometerwas in a range o 0.3 to 30 m/s, with accuracy o 0.1 m/s.

Te moisture was determined by use o the oven methodo drying in a dryer at 105 C or three hours up to constantmass with assumption that the sample, beside moisture, doesnot contain any other evaporative ingredients or products that

may cause variances in the mass o the studied sample (ukoand Petek, 1970). Te drying o the sample was perormedin the laboratory oven dryer (INKO S-40) with a acility toregulate temperature between 40 and 240 C. Te accuracyo measurement is 0.1 C, and working space volume was20 liters.

On the basis o the mass losses measurements, every veminutes the exponential equations were calculated in requiredtemperature values or each studied hybrid up to moistureequilibrium (6%). Mathematical modeling will give the valueo water release rate up to moisture equilibrium, in order to beable to exactly compare the variances in water release rate ospecic hybrids. In all obtained exponential equations it wasnecessary to nd the determination coe cient that shows thecomparability o the results o water release rom the seeds.

Te data was analyzed ollowing GLM procedure in theSAS system package in version 8.0 (SAS Institute, 1997). Teresults were subject to variance analysis, while the varianceso mean values were compared by use o LSD test or p=0.05.

Results and discussion

Te Figures 1, 2 and 3 show the drying curves specicallyor all three drying temperatures or the studied hybrids, orthe purpose o determining the relations between the hybridsand water release rate.

Kinetics o convection drying was studied or three hy-brids at three drying temperature variances. Te drying curvewithin individual hybrids have a normal course. When ki-netic drying curves were determined in diferent drying con-ditions, geometrically similar curves were obtained that arecharacteristic or the studied material.

It can be determined that, independently o temperature,hybrid Artus had the longest drying time, and itan had theshortest one, by 31% in average. At 40 C this percentage was28%, at 60 C 38%, and 25% at 80 C. At air temperature o40 C, it took hybrid Artus 95 minutes to dry, while at the


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air temperature o 60 C the drying time was 56% shorter.With the air temperature in the drying process o 80 C, thedrying time o hybrid Artus was 79% shorter in relation tothe rst air temperature.

At air temperature o 40 C, it took hybrid Baldur 85minutes to dry, while at 60 C this time was 65% shorter. At

drying air temperature o 80 C, the drying time or hybridBaldur was 83% shorter than with the rst air temperature.

Hybrid itan, at temperature o 40 C was dried aer 70minutes, while at 60 C it took 66% shorter time to dry. Tedrying time o hybrid itan at temperature o 80 C was 79%shorter than at 40 C.

In order to make the drying curves o the observed hybridscomparable, the mathematical modeling o equation o waterrelease rate was applied. A similar method was also used byMartins and Stroshine (1987), and Krika (1993). able 1 givesthe exponential equations o drying o the observed hybridsup to moisture equilibrium (6%). Te analysis o the dryingequations makes it evident that the exponential coe ciento variables has a negative sign, which means that the curvealls. Namely, it shows the tendency o the water release rate(able 1). With higher absolute value o the coe cient, thedrying rate was higher.

Aer ormulating the exponential equations the determina-tion coe cient was ound in the range between 0.86 and 0.97.

Such high coe cients show that the research o water re-lease rom the seeds was carried out with precision and thatthe obtained results can be compared with each other. Tecalculation o the water release coe cient allows to preciselydetermine which hybrid has the shortest and which one hasthe longest water release time.

able 2 presents the reaction rate constant values in waterrelease rom the seed up to constant moisture or all studiedhybrids. Te above able shows that at all temperature levels,hybrid itan had the astest drying rate, while hybrid Artushad the slowest one. Tereore, it can be determined that therapeseed hybrids perorm diferently in the drying process,

pending on drying temperature. Similar conclusions werereached by Krika et al. (1999). Teir researches also showedthe variations between the cultivars but also the variationsbetween the years o cultivation. Moreover, in this researchone o the hybrids (itan) had a higher drying rate thanothers, regardless o temperature level, which is very valu-able or drawing conclusions. Given the act that convectiondrying o the observed hybrids was carried out in one yearonly, it is not possible to claim with a great accuracy that theitan seeds would always have the highest draying rateamong this group o hybrids, should the research be carriedout over a several year period. Te seed drying coe cientsshowed that the highest value was observed in hybrid itan,

with 0.236 s-1, and the lowest one in hybrid Artus, where thecoe cient was 0.101 s-1. In accordance with the able aboveit can be concluded that the seed drying constant (k) signi-cantly grows with increasing air temperature, and it varieswith each studied hybrid.

Using the Arrhenius equation the curves were denedor interdependence between seed drying rate constant anddrying temperatures (Henderson and Pabis, 1961; Bala 1997).Te incline o the direction was the basis or determiningthe activation energy o the rapeseed hybrids. By calculat-ing the value o activation energy, it is possible to determine

0

2

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10

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18

0 20 40 60 80 100

Drying time (min)

Se

edmoisture(%)

Artus

Baldur

Titan

0

2

4

6

8

1012

14

16

18

20

0 5 10 15 20 25 30 35 40 45

Drying time (min)

Seedmoistu

re(%)

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BaldurTitan

0

5

10

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0 5 10 15 20 25

Drying time (min)

Seedmoisture(%)

ArtusBaldur

Titan

Figure 1. Drying curves or investigated hybrids at airtemperature o 40 C




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195Convective Drying o Rapeseed Hybrids Seeds

the energy that must be introduced in the seed by thermal

procedure o convection drying in order to stir molecules tointeract and to start the drying process.

As activation energy value is higher, the reaction slowsdown, i.e., the drying process is slower. Te able 3 presentsthe activation energy values or all studied hybrids, obtainedrom the analysis o water release rates at three drying tem-peratures.

Te largest amount o energy required to start the dryingprocess was observed in the hybrid Artus, 27.13 kJ/mol. It issignicantly above the values observed in other hybrids. Telowest activation energy value was observed in hybrid itan,

8.01 kJ/mol, while in hybrid Baldur it was 12.93 kJ/mol. It canbe determined that the variations in activation energy valuesamong the studied hybrids exist. Since the drying times alsoshowed the same tendency it can be determined that the ac-tivation energy directly depends on water release rate. Tesame conclusion was also drawn by Bala (1997).

Conclusions

On the basis o this research, the results o drying o theseed o rape hybrids Artus, Baldur and itan the ollow-ing conclusions can be drawn:

1. Exponential equations o drying are comparable or spe-cic drying temperatures and showed the variations inwater release rates in seed o all studied hybrids.

2. In all exponential equations high determination coe -cients were ound showing that the selected model wasappropriate and the results were comparable. By compar-ing the exponential equations and seed drying constantsit was observed that hybrid Artus had the slowest drying,and itan perormed the astest drying.

3. Te study showed statistically signicant (P = 0.01) di-erence between water release rates in the studied hybridsin convection drying o seeds. Te hybrids show difer-ent perormance under the same drying conditions. Byincreasing the air temperature, the seed water release rateincrease becomes statistically signicant (P = 0.001).

4. Te highest activation energy required or starting thewater release rom seed was ound in hybrid Artus, andthe lowest one in itan. Accordingly, it can be conclud-ed that activation energy is in inverse proportion to seedwater release rate.

ReferencesBala B.K. (1997). Drying and Storage o Ceral Grains, Science

Publisher, New Hampshire, SAD.BIOEN (2001). Projekt Biodizel uvoenje proizvodnje

biodizelskoga gorvia u Republiku Hrvatsku, Studijaizvodljivosti, Energetski institut "Hrvoje Poar", Zagreb.

Henderson S.M., Pabis S. (1961). Grain drying theory: Iemperature efect on drying coe cient, Journal o AgriculturalEngineers Research 6(3): 169-174.

Kati Z. (1997). Suenje i suare u poljoprivredi, Multigra, Zagreb.Krika . (1993). Utjecaj peroriranja pena kukuruza na brzinu

suenja konvekcijom, Doktorska disertacija, Agronomskiakultet, Zagreb.

Krika ., Juki ., Voa N., Mileti S. (1999). Komparativnaanaliza suenja sjemenki uljane repice "00" kultivara Silvia i"00" kultivara Diana, Karola, Semu 910201, Semu 93-10 i Lirajet,Poljoprivredna znanstvena smotra, 64(2): 113-121.

Krika ., Voa N., Juki ., Ki D., Voa S. (2005). Disturbancesin the Process o Corn Grain Cooling in the Vertical GravityDryers, Strojniki vestnik Journal o mechanical engineering,51(4): 204-216.

Krika ., Voa N., Janui V., omi F., Juki ., Matin A.(2007). Inuence o reatment and Storage o Rapeseed onits Properties as a Raw Material or Biodiesel Production,Poljoprivredna znanstvena smotra, ematski broj, 2ndInternational and 19th Croatian Congress o echnologists orPost-harvest echnology, 72(3): 173-176.

Hybrid Artus Baldur Titan

Activation energy (kJ/kg) 27.13a 12.93c 8.01b

Coefficient of seed drying, k (s-1)Drying temperature (C) Artus Baldur Titan40 0.082a 0.097b 0.171b60 0.090a 0.100ab 0.239ab80 0.128a 0.169a 0.299aMean value 0.100 0.122 0.235LSD NS ** ***Hybrid (H) **ArtusBaldurTitan

0.101b0.122b0.236a

Drying temperature (T) ***40C60C80C

0.116c0.143b0.199a

H x T NS**, *** - significance at the 0.01 and 0.001 probability level, NS not

significant The differences between the values with the same letters arestatistically insignificant at P=0.05

Hybrid Drying temperature (C) Exponential equation R2

40 y = 18.972e-0.0097x 0.97

60 y = 19.564e-0.0246x

0.95

Artus

80 y = 16.89e-0.0512x 0.9640 y = 16.49e-0.0104x 0.9560 y = 16.465e-0.0313x 0.93

Baldur

80 y = 15.397e-0.0637x 0.9640 y = 16.344e-0.0101x 0.9760 y = 16.045e-0.0323x 0.91

Titan

80 y = 14.461e-0.0657x 0.86

y seed moisture (%), x drying period (min)

Table 1. Exponential equations o seed drying up to constantmoisture (6%) or the studied hybrids at three diferent dryingtemperature

Table 2. Values o reaction rate constant in drying (k) oseeds up to constant moisture (6%) o studied hybrids at threedrying temperature levels

Table 3. Mean values o activation energy o the studiedhybrids


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Martins J.H., Stroshine R.L . (1987). Diference in drying E cienciesAmong corm hybrids dried in a high temperature column natchdryer, ASAE Paper No 87, St Joseph, SAD.

Mujumdar A. (2000). Drying echnology in Agriculture and FoodScience, Science Publisher, Plymouth, UK.

Noomhorn A., Vermal R. (1986). A Generalized Single-layer RiceDrying Model, ASAE American Society i AgriculturalEngineers, St. Joseph, Michigan, 86: 305-307.

Page C. (1949). Factors inuencing the maximum rates o dryingshelled corn in Layers, Ms Tesis, Department o AgriculturalEngineering, Purdue University West Laayette.

Pliesti S., Varga B. (1995). Utvrivanje lomne otpornosti prirodnovlanog i rehidriranog zrna kukruza Bc 492, Zbornik radova,XI. Meunarodno Savjetovanje tehnologa suenja i sk laditenja,Stubike oplice, 113-124.

Sander A., Glasnovi A. (2004). Procjena karakteristinih veliina uprocesu suenja, Kem. Ind. 53(3): 109-115.

SAS Institute (1997). SAS/SA Soware: Changes andenhancements through Rel. 6.12. Sas Inst., Cary, NC, SAD.

uko A., Petek M. (1970). Analize i poznavanje stone hrane, Centarza primjenu nauke u poljoprivredi SRH, Zagreb, 207-220.

Tompson .L. (1967). Predicted Perormance and optimal design

o convection in Grain Dryers, PhD Tesis, Department oAgriculture, Kansas State University, SAD.Voa N., Krika ., Matin A., Janui V., Juki ., Kievi M. (2007).

Activation Energy o Water Release Rate rom Corn KernelDuring Convective Drying, Poljoprivredna znanstvena smotra,ematski broj, 2nd International and 19th Croatian Congress oechnologists or Post-harvest echnology, 72(3):199-204.

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